Gas testing



May 2, 1939- M. G. JACOBSON GAS TESTING Filed Nov. 12,

1956 2 Sheets-Sheet 1 INVENTOR.

BY 5M, aym aw ATTORNEYS.

May 2, 1939.

M. G. JACOBSON GAS TESTING 2 Sheets-Sheet 2 Filed Nov. 12, 1936 INVENTOR.

ATTORNEYS.

ant electromotive force created between that electrode the Product Of the action of the gas 45 Patented May 2, 1939 J 15% UNITED STATES PATENT OFFIE GAS TESTING Moses G. Jacobson, Swis'svale, Pa., assignor to Mine Safety Appliances Company, Pittsburgh, Pa., a corporation of Pennsylvania Application November 12, 1936, Serial No. 110,506

21 Claims. (01. 23232) This invention relates to gas testing, more reaction. In the cell one of the electrodes is particularly to a method and apparatus for the maintained continuously wholly submerged in detection and quantitative determination of parthe electrolyte, and the other electrode is so articular constituents present in gases or gas mixranged that a portion of it may be exposed to tures'. the gaseous constituent and the remainder sub- 5 It is among the objects of the invention to merged in the electrolyte. When the gaseous provide a method of gas testing whereby the atmosphere containing the constituent which presence or concentration, either or both, of a is reactive with the electrode is passed into conparticular constituent of the gas being tested tact therewith, there will be generated an elecmay be rapidly and readily determined, which tromotive force within the cell. 10 is simple, is satisfactorily accurate, and does not Where it is desired only to determine the presrequire complicated and. expensive apparatus, 7 ence of the constituent being tested for, the and in which the constituent to be determined E. M. F. of the cell is used to operate any suitis applied to the generation of an electromotive able electrical indicating means such as a galforce which is'a definite function of the convanometer or milliammeter, the needle move- 15 centration of that constituent, ment showing the presence of the constituent in f .A further object is to provide apparatus for the gas being tested- Or, it y be pl fied use in the practice of the method provided by or tu a r y means t p a an audi le the invention which is of simple and inexpenor visual signal.

- sive construction, which is readily used, portable, This as I have confirmed y tests, 20 and rugged; and whose operation does not re- 18 a fllIlCtiOn 0f the concentration 0f the COIL- quire scientific training Or experience. stituent in the gas mixture under test. There- The invention may be described in connection fore it y be applied directly to e e ent with the accompanying drawings in which Fig. of the concentration. For such purposes the best w 1 is a vertical sectional view through one emresults are attained y measuring e F- 25 bodiment of the apparatus provided by the in- Of the cell after the production of an equilibrium vention, and showing, schematically, an electribetween the reaction between the electrode and cal circuit particularly adapted to the practice gas 011 191160116 hand, and the p ce e t of of the invention; Fig. 2 a view similar to Fi 1 the reaction product from the electrode on the showing the parts in another position used in Other h d- This ay e a pl s ed 'in var- 3c the operation of the device; Fig. 3 a plan view 1 11 W s y h use Of a s na y partly of the device shown in Figs. 1 and 2; and Fig. immersed electrode, ap ry forces drawin 4 a vertical section through another embodithe electrolyte p into the region Of the elecment of the invention. trode which is acted upon by the gas, or by The invention is predicated in part upon my using a rotary electrode P y sed in the conception that the presence and concentration, e1e0tr01ytB, O in other ways which Will occur either or both, of a constituent of a gaseous atto those skilled in the mos'phere may be determined readily by contact- The electrodes Used are Composed of a ta ing the gas with an electrode formed of t a metallic alloy, or other solid conductor of elec- 40 rial which is reactive with that constituent and tricity which, either dir t y or afte bein 40 which is partly immersed in an electrolyte ca- W t w the electrolyte, is a d up by pable of destroyingor removing from the electhe gas whose presence or concentration is to trode the product of reaction between "the elecdetermined- The electrolyte, 011 the other trode and the gaseous constituent. The resulthand, Chosen that displaces fr the electrode and another similar electrode which thereoh- This displacement y be cfiected in is wholly immersed in the electrolyte is applied Various Ways, as through Chemical deco posito indicate the presence or concentration of the tion 0f e reaction product by the ytc, tit t, by dissolution of the product in or its desorption m More particularly, in accordance with the inby the electrolyte, or by other chemical or 5 vention there is provided a voltaic cell comprisp ys phenomena, a o evity all such. ing a pair of electrodes formed of material reacmodes -of displacement are comprehended by tive to the constituent which isto be determined, reference in some of the claims to solvent power and an electrolyte which is adapted to displace of the felectrolytelfor. the reaction products of e from the electrodematerial theproduct of such the gas and electrode. As an example, where 5 per, and the electrolyte may be a solution of various salts or other compounds, the exact com pound or combination of compounds used, and

their concentration, being governed by the particular use to which the instrument is to be trolyte may consist of a solution of ammonium hydroxide, or of ammonium chloride. Using ammonium hydroxide the absolute sensitivity is not as great as whenthe chloride is used, but the response greatly accelerated, and the shape of the calibration curve is such that relatively large deflections of the electric meter are produced in the low range of oxygen concentration. With an ammonium chloride solution the results are the reverse of those obtained with ammonium hydroxide. Thus it appears that low concentrations of oxygen may be determined suitably using an electrolyte consisting of ammoniumhydroxide in combination with a sensitive meter, while for analyzing compositions in which the oxygen content approaches that of pure air thereJmay be used a solution ofam monium chloride And for use over theentire range, the electrolyte may include both compounds.

In general it is desirable to add to the electrolyte a small amount of ammonium carbonate to decreasethe absorption of carbon dioxide, thus decreasing. the effect of carbon dioxide on the absolute sensitivity. I now prefer to use a solutionof ammonium chloride (NHiCl), ammonium product from the electrode.

In general, rather high dilution of the ,electrolyte is desirable because thereby the instrument keeps its sensitivity setting on air longer than where concentrated solutions are used, and electrode and electrolyte life is prolonged. The limit of dilution is .fixe'd by the sensitivity of the meter used, as will be recognized.

Having reference now to the drawings, Fig. 1 shows an apparatus embodying the principles which underlie the invention. It comprises a cell I in the form of a gas-tight case of electrically insulating material such as synthetic resin, hard rubber, glass, or other substances havlngsuita-, The cell is divided in ble dielectric properties. teriorly by a heavy partition Wall 2 forming compartments 3 and 4 which :areintercommunicating through passages}, 6 and 1.

supportedon shalts l3 and I4.

tionsshown in Figswland 2.

, the cell through passage 1 into a conduit 2|.

.1 highly consta nt. H Theele'ctrornotive rorce generatedby the cell i Compartment 3, suitably of cylindrical section, is provided with screw-threaded upper'and lower closure members 8 and 9, respectively. Disposed in compart" ment 3 are two ring-shaped electrodes "land I! spaced vertically from each other. -Mounted in. compartment 4 is a plunger member l2 rotatably Shaft" extends through ages-tight paeking, gland t5 and on its; outer end is'mounted a crank member I6 having acrank pin 1 1 connected toa handle 18 for mov ing theplunger totthe raised and loweredp W V l In the use of thisapparatus an electrolyte I9 is placed in the cell in an amount such that when plunger 12 is in its raised position (Fig. 2)

electrode lll willbe partly submerged in the electrolyte, as seenin Fig. 2. When the plunger is lowered to the position shown in Fig. 1, however, it will displace theelectrolyte so that both electrodes are completely submerged. put. Thus, in.theinstancereferred to the elec-H Whenboth electrodesare submerged in the electrolyte no electroniotive "force will be generated between the electrodes and the electrolyte since the electrolyte will remove from the upper electrode any reaction product that has been i there will be no E. M. F. created.

In making a test plunger solution to the position shown in Fig. 2; and the gas to be tested is passed into theinterior of the cell through a conduit 20 which opens at its lower end into the cell, e. g., into passage 6. ,The gas circulates through the cell, contacts the exposed portion of electrode 10, and is withdrawn from In the embodiment shown an aspirator bulb 22 is used to draw the gas through the cell.

. If the gas contains the constituent with which the electrode is capable of reacting, the action between themwill begin and the cell will now formed betweenit and the gas to which the electrodes are. sensitive. When the electrodes 12 is raised from the consist of unchanged electrode H, the electrolyte 1 I IS, and electrode lilwhich consists partly of the originalmaterial and partly of the product of reaction of the electrodeand the gas, and accord-,- ingly an electromotive force will be generated.

Due to capillary forces the electrolyte will be drawn up over the exposed'portion of electrode lil andwill begin to exert its action upon-the reaction product formed on the electrode. In a The magnitude er the electromotive force under equilibrium: conditions, other. things being constant, dependsupon the concentration of the particular constituent which is being determined l in the gaseous atmosphere; Theabsolute sensitivity may change very slowly as the amount of .gas taken up by the electrolyte increases. However, extensive tests of the invention have shown that even though" the absolute values change as the reaction product is "taken 'up by the, electrolyte, the relative sensitivity, i. .e.,,the ratio of l the electromotive forces corresponding to two given concentrations of gaseou su constituent is may be determined invarious ways. "As stated,

. itm'ay be usedto merely indicatethe presence of the constituent,yoritmaybe used fora quantitative determination .as through the use of a Wheatstone bridge or ,potentiometercircuit. In

the circuit shown in themilliammeter 23 is' connected by a wire 24 to electrode I0, and

electrode I! .is connected by a wire 25 to the being determined;

anew dr he e ristaney ortn ratio o mi apprepriate ,peint ef circuit. The scale of the milliammeter is conveniently, calibrated in terms of'the concentration of the constituent.

liammeter deflections corresponding to two given concentrations of gaseous constituent, the circuit includes a rheostat 26 connected in series with the millivoltmeter. Before making a test the instrument is calibrated, and where oxygen is being determined atmospheric air is used for that purpose. To this end air is aspirated through the cell by bulb 22 and plunger I2 is turned into its up position (Fig. 2). When the pointer of the milliammeter has come to rest it is adjusted by means of rheostat 26 to show 21 per cent of oxygen on the scale. The plunger is then turned into its down position (Fig. 1) until the pointer has come back to zero, due to complete removal of oxidation product from electrode I0, thus putting both electrodes in identical condition. The gas to be tested is then aspirated, the plunger turned up, and when the pointer has come to its rest position the concentration of gas is read directly on the scale of the meter. A complete test, including the calibration on air, can be completed in not more than about five minutes. of course, with other gases than oxygen, known concentrations in a gas mixture are used to calibrate the instrument.

In order to avoid waiting for the pointer to return exactly to zero in case of small differences in the electrodes, the circuit has been specially arranged for zero adjustment. With this circuit when the pointer with the plunger in the down position does not come back to zero within a brief interval, say two minutes, it is adjusted to zero by means of a rheostat 27. The circuit shown will operate on a small No. 2 dry cell which will last for at least six months.

When the determinations are completed, say at the end of the day, the cell should be thoroughly cleansed. To this end closure members I and 8 are so arranged as not to restrict the openings in chamber 3, thus permitting easy flushing out, cleaning and drying of the chamber and the electrodes.

Another embodiment of the invention is shown in Fig. 4. This comprises a cell 30 of electrically insulating material provided with an inlet BI and an outlet 32 for the gas to be tested. The cell is provided also with upper and lower closure members 33 and 34, respectively. Disposed toward the lower end of the cell is a ring electrode 35 mounted to be continuously wholly submerged in the electrolyte 3t. Mounted thereabove is a disc electrode 31 of the same material mounted vertically one, shaft 38which may be rotated by any suitable means, not shown. Shaft 38 passes through a gas-tight packing gland 39. The electromotive force generated in the cell is passed by wires 40 and M to any suitable measuring means or circuit, the current being taken from shaft 38 in any suitable manner as by a slip ring and a contact brush indicated schematically at 42 and 43.

In the use of thisapparatus electrode 31 is rotated continuously, thus progressively and continuously moving the exposed portion with its reaction product downwardly into the electrolyte which removes the reaction product, those por-v tions of the electrode which have been thus cleaned moving progressively and continuously upwardly into the gas space for further reaction with the gas. In this manner the equilibrium condition is achieved without dependence upon capillary forces and without the use of special means for raising and lowering the level of the electrolyte. The electrodes may take a variety of forms, as

i of a particular gas.

will be realized. For instance, they may be formed of wire gauze or of imperforate material, and they may consist of pure metal or metallic alloy, or of other'solid conductor or semi-conductor such as carbon or a salt, or they may be formed by compressing a powdered salt or impregnated charcoal. They may be in the shape of rings, which are especially suitable in apparatus of the type shown in Figs. 1 to 3, or, as in the apparatus shown in Fig. 4, the electrodes may take the form of circular discs.

The apparatus shown in Fig. 4 has the further advantage, as contrasted with that shown in Figs. 1 to 3, that by varying the speed of rotation of electrode 31' and the ratio of the portion of the electrode submerged in the electrolyte to that exposed to the gas, there is much wider control over the equilibrium point between the reaction and displacement, and better control over sensitivity and scale characteristics.

Although reference has been made herein to determination of a particular constituent of a gaseous atmosphere or mixture, it will be understood that the invention is applicable not only to the determination of the presence or concentration of a given constituent of a true gaseous mixture, but also to the determination of the purity The invention is likewise not restrictedto the determination of oxygen which has been referred to herein purely by way of illustration, not by way of limitation. As will be understood, it is equally applicable to the determination of other gases, such as chlorine, hydrogen sulfide, and others, by appropriate selection of the electrode and electrolyte materials, which can be done by those skilled in the art. Thus, for the determination of hydrogen sulfide (Has), there may be used electrodes of magnesium (Mg) and an electrolyte formed of a very weak solution of sulfuric acid (H2304). The hydrogen sulfide forms magnesium sulfide atthe exposed portion of the electrode, and this reaction product is dissolved in the electrolyte when the electrode is submerged therein. The small amount of sulfuric acid present prevents the electrolyte from absorbingany considerable amount of hydrogen Again, in the determination of chlorine there may be used tin (Sn) electrodes and an electrolyte consisting of a weak aqueous solution of ammonium stannic chloride ([NH412SDC16) and ammonium chloride (NI-IrCl). The tin and chlorine react to form stannic chloride (SnClr) which upon submersion of the electrode is con verted to ammonium stannic chloride and dissolved.

Various additions or alterations may be made in the method and apparatus described without departing from the inventon. Thus, the E. M. F. of the cell may be used to actuate recording or control mechanism. Similarly, a pump may be usedto force the gassample through the cell, and the rotatable plunger of the apparatus shown in Figs. 1 to 3. may be replaced bya vertically reciprocable plunger.

Also, while it is preferred now to form both electrodes of the same material, because electrical neutrality may thus be reached as described hereinabove, it will be understood that the submerged electrode may be made from a material which is not attacked, such, for example, as gold. In such event the E. M. F. of the cell will not be zero when the active electrode issubmerged but the meter pointer can be adjusted to zero by means of the electrical balancing circuit, as will exposed electrode part.

utes, I have explained the principle and mode of construction and operation of my invention, and have illustrated and described what I now con-' sider to be its best embodiment. However, I desire to have it understood that, within the scope of the appended claims the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. In a gas testing apparatus the combination of a container, a pair of electrodes disposed in spaced relation therein and adapted for connection to electromotive force measuring means one of said electrodes being formed of a material reactive with the gas to be determined, an electrolyte in said container adapted to displace from i said reactive electrode reaction product of said gas and said material, and said reactive electrode being positioned to have a part exposed to gas sample and part immersed in said electrolyte, means for contacting said exposed electrode part with said electrolyte, and means for passing gas into said container into contact with said 2. In a gas testing apparatus the combination of a container, a pair of electrodes disposed in spaced relation therein and adapted for connection to electromotive force measuring means,

said electrodes being formed of a material reactive with the gas to be determined, an electrolyte in said container adapted to displace re- 7 action product of said gas and said material, one

of said electrodes being continuously covered by said electrolyte, and the other electrode being positioned to have a part exposed to gas sample and part immersed in said electrolyte, means for periodically covering said exposed electrode part with said electrolyte, and means for passing gas into said container into contact with said exposed electrode part.

3. In a gas testing apparatus the combination of a gas-tight container provided with gas inlet and outlet openings, a pair of electrodes disposed in spaced vertical position therein and adapted for connection to electromotive force measuring means, said electrodes being formed of a material reactive with the gas to'be determined, an

electrolyte in said container adapted to displace reaction product of said gas and said material,

the lower of said electrodes being continuously covered by said electrolyte, means disposed in said container for changing the level of said electrolyte to cause the upper electrode to be alternately completely covered and then to have a part exposed to gas sample and part immersed in said electrolyte, means disposed exteriorly of said container for actuating said level-changing means, a connection between said actuating and level-changing means extending in gas-tight relationship througha Wall of said container, and means associated with said gas inlet opening for passing gas into said container into contact with said exposed electrode part.

4. In a gas testing apparatus the combination of a container, a stationary electrode disposed in said container, a rotary electrode disposed in the container above said stationary electrode, said electrodes being formed of material reactive with the gas to be determined, an electrolytein said container adapted to displace reaction product of said gas and said 'material, said stationary electrode being continuously covered by said elecbe understood fromwhat has been said hereinabove. According to the provisions of the patent stattrolyte, and said rotary electrode being positioned to have a part exposed to gas sample and part immersed in said electrolyte, andgneans for passing, gas into, said container into, contact with said exposed electrode part.

means disposed in the container for raising and lowering the electrolyte level to alternately completely cover the upper electrode and then to have apart of it exposed to gas sample and part immersed in said electrolyte, means disposed exteriorly of said container for actuating said plunger, a connection between said actuating means and plunger extending in gas-tight relationship through a wall of said containenand means associated withsaid gas inlet opening for passing gas into saidcontainer into contact with said exposed electrode part. 1

6. In a gas testing apparatus the combination of a gas-tight container provided with gas inlet and outlet openings and with a pair of intercommunicating compartments, a pair of electrodes disposed in spaced vertical relationin one of said compartments and adapted for connection to electromotive force measuring means, said electrodes being formed of material reactive with the gas to be tested, an electrolyte in said compartments adapted to displace reaction product of said gas and electrode material, and means disposed in the other of said compartments for causing the upper electrode alternately to be exposed in part to gas sampleyand then to be wholly submerged in the electrolyte, while continuously maintaining the lower electrode continuously submerged, means disposed exteriorly' of said container for actuating said electrodesubmerging means, a connection between said actuating andelectrode-submerging means exlation in said circular section compartment and adapted for connection to electromotive force measuring means, saidelectrodes being formed of material reactive with gas to be determined,

an electrolyte in said'containeradapted to displace reaction product of said gasand electrode material, a plunger in the larger of said compartments for causing the upper electrode alternately to be exposed in part to gas sample, and then to be wholly submerged in the electrolyte, While continuously maintaining the lower electrode continuously submerged, means disposed exteriorly of said container for actuating said plunger, a connection between said actuating and plunger means extending in gas-tight relationship through a wall of said container, and means associated with said gas inlet opening for passing 11. In a gas testing apparatus, a voltaic cell inas sample into said container for contact with the exposed electrode part.

8. In a gas testing apparatus the combination of a container, a pair of electrodes disposed in spaced relation therein, one of said electrodes being formed of a material reactive with the gas to be determined, an electrolyte in said container adapted to displace reaction product of said gas.

and said material, one of said electrodes being continuously covered by said electrolyte, and said reactive electrode being positioned to have a part exposed to gas sample and part immersed in said electrolyte, means for contacting said exposed 'electrode part with said electrolyte, means for passing gas into said container into contact with said exposed electrode part, and electrical indicating means comprising an electrical meter, connections between said electrodes and meter, and

a variable rheostat in said circuit for adjusting the meter to indicate a definite value when a standard gas concentration is admitted to the container.

9. In a gas testing apparatus the combination of a container, a pair of electrodes disposed in spaced relation therein, one of said electrodes being formed of a material reactive with the gas to be determined, an electrolyte in said container adapted to displace reaction product of said gas and said material, one of said electrodes being continuously covered by said electrolyte, and said reactive electrode being positioned to have a part exposed to gas sample and part immersed in said electrolyte, means for contacting said exposed electrode part with said electrolyte, means for passing gas into said container into contact with Said exposed electrode part, and electrical means comprising an electrical meter, a source of electromotive force, a variable rheostat, circuit connections between said source of electromotive force, electrodes, rheostat, and meter forming a circuit in which a part of the voltage from said source may be added to or subtracted from the voltage between said, electrodes, and a second variable rheostat connected with said meter to adjust its indication to a definite value when a standard gas concentration is passed into the container.

10. In a gas testing apparatus the combination of a container, a pair of electrodes disposed in spaced relation therein, one of said electrodes being formed of a material reactive with the gas to be determined, an electrolyte in said container adapted to displace reaction product of said gas and said material, one of said electrodes being continuously covered by said electrolyte, and said reactive electrode being positioned to have a part exposed to gas sample and part immersed in said electrolyte, means for contacting said exposed electrode part with said electrolyte, means for passing gas into said container into contact with said exposed electrode part, and electrical means comprising an electrical meter, a source of electromotive force, a variable potentiometer rheostat, two constant resistances, and circuit connections forming a Wheatstone bridge of said potentiometer rheostat and said two constant resistances, said electrodes and meter being included in one cross arm, and said source of electromotive force in the other cross arm, and a variable rheostat connected with said meter to adjust its indication to a definite value when a standard gas concentration is passed into the container.

cluding a container, a pair of electrodes disposed in said container and adapted for connection to an electromotive force measuring means, one of said electrodes being reactive to the gas to be determined, an electrolyte in said container adapted to remove from said reactive electrode product of reaction thereof with said gas, said reactive electrode being positioned relative to said electrolyte to have a portion exposed to gas to be tested, means for periodically wetting said exposed portion with said electrolyte, and means associated with said container for passing gas into contact with said exposed electrode portion.

12. That method of testing gas which comprises providing a voltaic cell including an electrode formed of material reactive with gas to be determined, andan electrolyte adapted to displace from said electrode product of reaction of said gas therewith, said electrode being partly immersed in said electrolyte; passing gas into contact with the exposed portion of said electrode,

and determining the electromotive force created to be determined, and an electrolyte which acts as a solvent for product of reaction of said gas with said electrode, said electrode being partly immersed in said electrolyte; passing gas into,

contact with the exposed portion of said electrode, bringing product of reaction of said gas and electrode into contact with said electrolyte, and determining the electromotive force created by said cell in consequence of such treatment.

14. That method of testing gas which comprises providing a voltaic cell including an electrode formed of material reactive with said gas to be determined, and an electrolyte which acts as solvent to product of reaction of said gas with said electrode, said electrode being partly immersed in said electrolyte; passing gas into contact with the exposed portion of said electrode, immersing the reacted portion of said electrode in said electrolyte, and determining the electromotive force created by said cell in consequence of such treatment.

15. That method of testing gas which comprises providing a voltaic cell including an electrode formed of material reactive with said gas to be determined, and an electrolyte which acts as solvent to product of reaction of said gas with said electrode, said electrode being partly immersed in said electrolyte; passing gas into contact with the exposed portion of said electrode, then wetting said portion of said electrode with said electrolyte, and determining the electromotive force created by said cell when equilibrium has been established between reaction of said electrode and said gas and displacement of reaction product from said electrode by the electrolyte.

16. That method of testing gas which comprises providing a voltaic cell comprising two electrodes formed of material reactive with said gas tobe determined, and an electrolyte which acts as sol vent to product of reaction of said gas with the electrode material, one electrode being partly immersed and the other electrode being wholly submerged in said electrolyte; passing gas into contact with the exposed portion of said one electrode, wetting said exposed portion with said electrolyte, and determining the electromotive force created by said cell when equilibrium has been established between reaction of gas and said electrode and displacement of reaction product from said electrode by said electrolyte.

17. That method of testing gas for a constituent thereof which comprises providing a voltaic cell comprising an electrolyte and a pair of electrodes one of which is continuously wholly submerged in said electrolyte and the other of which is partly immersed in said electrolyte and is formed of material reactive with said constituent, said electrolyte acting as solvent to product of reaction between said constituent and said other electrode; alternately exposing a portion of said other electrode to said gas and then wholly submerging it in the electrolyte, and measuring the electromotive force created by the cell during such treatment when equilibrium has been attained between said reaction and the solution ofreaction products by said electrolyte.

18. That method of testing gas for a constituent thereof which comprises providing a voltaic cell comprising an electrolyte and a pair of electrodes one of which is continuously wholly submerged in said electrolyte and the other of which is partly immersed in the electrolyte and is formed of material reactive with said constituent, said electrolyte acting as solvent to product of reaction between said constituent and said other electrode; contacting the exposed portion of said other electrode to said gas, rotating said other electrode while maintaining contact of gas with said exposed portion, and measuring the electromotive force created by the cell during such treatment when equilibrium has beenattained between said reaction and the solution of reaction products by said electrolyte.

19. That method of testing gas for oxygen which comprises providing a voltaic cell including, as an electrolyte, an aqueous solution of 'am monium compounds capable of dissolving copper oxide, and including also a pair of copper electrodes one of which is partly immersed in said electrolyte; Wetting the exposed portion of said one electrode with said electrolyte and then alternately passing the gas into contact with the exposed portiontof said one electrode and then wetting said exposed portion by said electrolyte, and measuring the electromotive force developed by the cell when equilibrium between reaction of oxygen on said exposed portion and displacement of resultant oxidation products from said portion by said electrolyte has been attained.

20. That method of testing gas for a constituent thereof which comprises providing a voltaic cell comprising an electrolyte and a pair of elecmeasuring the electromotive force created by the cell when equilibrium has been attained between reaction of the'gas and said electrode portion and the solution of reaction products therefrom by said electrolyte.

21. A method according to claim 19, said electrolyte comprising ammonium carbonate, ammonium chloride, and ammonium hydroxide, and a small quantity of ammonio-cupric ions.

MOSES G. JACOBSON. 

